Whether you’re training for your latest 10K fun run or out for a well-earned family day at the beach, it’s important to protect your skin from the sun. That includes applying sunscreen before you head out. But are you confident that your sunscreen will stand up to the sweat and surf that you will inevitably encounter? Here, we’ll discuss how and why to choose a water resistant sunscreen.
As the name suggests, water resistant sunscreen is designed to remain effective when swimming or taking part in other water-based activities, or during activities that make you sweat. These sunscreens are less likely to be removed from the skin by water or sweat because they are formulated with special ingredients called polymers that help them stick to the outermost layer of skin and resist removal by water.
However, it’s important to understand what exactly is meant by the term ‘water resistant’. For any sunscreen to be labelled as water resistant, it must pass testing that shows it retains a specified sun protection factor (SPF) rating after being immersed in water for a certain amount of time.
First, what is an SPF? Essentially, the SPF measures how well a sunscreen protects your skin against ultraviolet (UV) radiation, specifically UVB radiation that is responsible for visible skin damage (sunburn). A sunscreen’s SPF is determined in a laboratory following a standard test procedure where small areas of volunteers’ skin are exposed to intense artificial UV light – one area is left unprotected, while another area is covered with exactly 2 milligrams per square centimetre of the sunscreen. The time taken for each area of skin to become red is measured, and the ratio of protected to unprotected skin is calculated to give the SPF value. In New Zealand, the highest SPF rating is 50+, which blocks 98% of UVB radiation when applied correctly.
The test for water resistance also involves applying sunscreen to a small area of volunteers’ skin and then immersing this area into water for a designated amount of time. The area of skin is then air-dried and subject to SPF testing as described above. The time limit for water resistance indicated on a sunscreen’s label reflects the total time the test areas of skin were immersed in water. In New Zealand, only sunscreens that achieve a SPF of over 30 after immersion in water can claim water resistance for up to 4 hours. Sunscreens that achieve a SPF of 16 to 30 after immersion in water can claim water resistance for up to 2 hours.
The other key thing to remember is that water resistant does not mean waterproof! Sunscreen will not stay on your skin forever once you get in the water or start your sweat-inducing workout and can also be rubbed off when you towel off after swimming or exercise.
During swimming and other water-based activities, sunscreen will inevitably wash off. And being in the water itself does not protect your skin from harmful UV radiation – around 40% of UV radiation can penetrate up to half a meter below the surface of the water – and the refreshing cool water could lull you into thinking that you’re not getting sunburned. UV radiation can also reflect off water as well as surfaces such as sand and concrete that go hand in hand with beach days or swimming carnivals. Using a water resistant sunscreen that is specially formulated to stay on wet skin for longer than regular sunscreen can help protect your skin against UV damage while you’re in and around the water.
But water resistant sunscreen is not just important when you hit the water. When you’re outdoors in New Zealand – whether it’s just hot and humid or you’re putting in 100% at bootcamp – you’re highly likely to sweat. And while sadly there’s no magic sunscreen that can stop you sweating, using a water resistant sunscreen can help keep your skin protected while you exercise.
While some water resistant sunscreens may last longer in salt water or chlorinated pool water than others, it’s highly dependent on the individual formulation. So as well as choosing a water resistant sunscreen with a high level of broad spectrum SPF50+ protection, the key to effective skin protection is to apply generous amounts of sunscreen correctly and regularly.
Did you know that many people don’t apply sufficient sunscreen to achieve the SPF level indicated on the label? To ensure full coverage, you should apply 30 mL to 40 mL – that’s about a full cupped adult hand of sunscreen – for an adult body. That works out to about 1 teaspoon of sunscreen per arm, leg, front and back of the body, and the face and neck.
You should reapply water resistant sunscreen at least every 2 hours but because sunscreen will wash or rub off during swimming or sweating, consider reapplying to dry skin immediately after getting out of the pool or surf or after you finish your outdoor workout. Always remember to wait 20 minutes after reapplying sunscreen before heading back into the sun or water!
When you’re looking for a great water resistant sunscreen to protect your skin, reach for INVISIBLE ZINC Sport Mineral Sunscreen. It contains micronised zinc oxide that delivers the highest SPF50+ broad spectrum UVA plus UVB coverage in a lightweight, non-greasy, low irritant formulation that’s suitable for sensitive skin and children.
Water resistant sunscreen is specially formulated with ingredients that help it stay on the skin longer during activities such as swimming or exercising when the skin is exposed to water or sweat.
Water resistant sunscreens must demonstrate a SPF rating of 30+ after being immersed in water for up to 4 hours. All sunscreens will eventually wash off in the water, so there is really no such thing as a waterproof sunscreen.
Water resistant sunscreens should be applied generously to all exposed skin 20 minutes before heading into the water or sun and should be reapplied at least every 2 hours. For the best protection, reapply to dry skin after swimming, sweating, or towelling off.